1. Field of the Invention
The invention lies in the signature transport and printing fields. Specifically, the invention relates to a positive control transport assembly such as used in a lower folder of a printing press assembly which positively controls a signature stream that is being diverted into two or more signature conveying streams.
A stream of printed products may be transported by a commonly known gripper conveyor. It is often desirable to split the common method of splitting a stream of products is to drag the initial stream over a vacuum belt traveling slower than the conveying system and to release every other signature from the gripper conveyor as soon as the respective signature contacts the vacuum belt. However, once the sheets are released their placement onto the vacuum belt fall according to a distributed pattern and the exact placement of the signature on the belt is not known. Consequently, correct alignment and a fixed pitch (a distance between the leading edge of two consecutive signatures in a product stream) of the signatures delivered to the vacuum belt cannot be guaranteed.
2. Description of the Related Art
U.S. Pat. No. 5,740,900 to Cote et al., for instance, describes an apparatus for splitting a product stream that includes a single conveying belt having a plurality of grippers traveling along a single conveyor path into two product streams. At least one of the grippers is capable of rotating a held signature from one side of the belt to the other side, so as to create a second parallel product stream. In this manner a single conveying belt forms two side by side product streams and at all times maintains positive control over the signatures. In this device the signatures are never released such as onto a vacuum belt that leads to the above mentioned distortions or pitch problems.
U.S. Pat. No. 5,560,599 to Curley et al. describes a deceleration device for slowing down signatures being transported in a folding machine. The deceleration device has a deceleration drum provided with a plurality of rotary grippers that positively grip an edge of the signatures exiting a tape conveyor system in the folding machine traveling at a high velocity. The grippers and drum decelerate the signatures before releasing them over a delivery stack.